Existing tool handles for manual household and industrial tools come in a variety of shapes and sizes. Often such handles are in the shapes of cylinders or polygonal prisms. When using such tools, the end of the cylinder or polygonal prism is usually pressed into the pocket in the palm of the hand. This pressing of the tool handle into the palm of the hand is illustrated in FIG. 1 for a prior art terminal insertion hand tool of the type often used in industry for manufacturing appliances and other electronic products. These terminal insertion hand tools are used to connect wires ends or "spades" into the sockets or "terminals" in the body of the appliance or other electronic product.
As the end of a cylindrical or polygonal prism tool handle is pressed into the palm of the hand, it will often cut off blood flow through the atrial arch of the palm, pinch the median, radial and ulnar nerves and compress the tendons which close the hand. This cutting off of blood flow and nerve pinching can create a numbness and tingling sensation in the fingers of the hand. If such a prior art tool is used repeatedly, such as in an appliance manufacturing operation, the continued assault on the blood vessels and nerves in the palm of the hand can lead to several adverse medical conditions, including carpal tunnel syndrome.
A number of efforts have been made to try to alleviate the causes of these adverse medical conditions by redesigning the tool handle. For example, tool handles have been made in a bulb-like shape to avoid sharp cylinder or polygonal prism edges pressing into the palm of the hand. One of these bulb shaped "ergonomic" handles is illustrated in Ballole's U.S. Pat. No. 4,448,460. Nonetheless, while such a bulb shaped handle alleviates a number of the problems that use of sharp edged tools can create in the palm of the hand, a bulb shaped handle nonetheless can create a different set of nerve and blood vessel pressure problems. It creates these problems by requiring the wrist to bend back as the palm of the hand presses on the bulb. This bending back of the wrist can place extreme pressure on the median nerve and impair hand performance.
U.S. Pat. No. 4,631,853 to Brackett et al. discloses a contoured fishing rod handle with an outwardly curved, laterally offset projection on one side of the butt grip, and an outwardly curved, laterally offset complimentary projection on the same side of the reel seat segment as the butt grip. The fishing rod handle of Brackett et al. is designed to resist twisting, and not intended as a tool to exert longitudinal pressure.
German Patent No. 23 44 987 to Weber discloses a hand tool with a bulbous grip and indentations for the fingers.
U.S. Pat. No. 4,038,719 to Bennett discloses a tool handle comprising an elongated member with a grip at one end, wherein the grip is 15 to 25 degrees displaced from tool shaft.
What is needed in the art is a tool handle which avoids stressing the nerves, blood vessels and tendons of the hand by keeping the hand in a neutral position and distributing longitudinal tool forces evenly throughout the hand and arm of the user.